Does marginally changing a well established domains URLs and page content affect site ranking in search engines

I am rewriting a web application and will be porting procedural PHP code to a framework.

At the same time, the layout of the pages (but not the critical content) is not changing.

I'm thinking that I need to some how port the old URLs by using a 301 Redirect permanent.

Any advice on how to proceed? As this site is long established with a good reputatio开发者_如何学Pythonn, it's important we maintain rankings in Bing and Google.

Thanks.

You should use 301 redirects instead, that will carry over the data the engines have for those pages and you should be fine